Solenoid-operated directional control valves are well known in the art having wide applications in both mobile and industrial uses. Such valves provide high flow capacity with small space requirement. Such valves utilize spring biasing means for biasing the spool to preselected positions for repositioning thereof by the action of the solenoid operator.
In one improved form of such control valves, the valve is shipped to the customer as a group of subassembly components. Thus, the valve may be provided with the coil, spool, valve block, and spring subassembly shipped separately. This permits the user of the valve to select any one of a plurality of different spools, coils, and spring subassemblies for use in a given control valve configuration.
It has been common to provide the spring subassembly as separate mounting tube, washer, and spring elements. The user selects the desired spring and installs it in the tube element. The washer is then placed in the assembly for cooperation with the spool when installed in the valve structure. Permitting the spring to be selected at the time of installation affords the user a wide range of possible valve configurations with minimum inventory.
However, the mounting of the spring and washer involves a somewhat difficult assembly procedure, and if not properly carried out, causes malfunctioning of the valve.
Another problem found in the prior art solenoid-operated spool valve structures is the presence of a pressure drop across the spool tending to oppose the return of the spool to the neutral position by the spring means upon de-energization of the solenoid coil. One of the causes of such pressure differential is the flow restriction of the tank port. Thus, it has been common to utilize a relatively large tank port diameter. However, in the prior art valves, this has necessitated correspondingly increasing the size of the valve body to accommodate the large tank port size.